1. Technical Field of the Invention
The present invention relates generally to an electrical starter which may be employed to start automotive engines, and more particularly to such a starter equipped with an impact absorber disposed between a planetary gear train and an overrunning clutch to absorb undesirable impact energy.
2. Background Art
Japanese Patent First Publication No. 63-277859 discloses an engine starter for automotive vehicles which is equipped with a impact absorber. FIG. 4 shows such an engine starter. The impact absorber installed in the engine starter is made up of a center casing 100, a stationary disc 110 secured fixedly to the center casing 100, and a rotary disc 120 interposed between the center casing 100 and the stationary disc 110 in frictional contact therewith. The rotary disc 120 is fitted at an end thereof within a groove 131 formed in an internal gear 130 to be rotatable together with the internal gear 130 relative to the center casing 100. When an impact torque higher than a specified level is added undesirably to the rotary disc 120 through the internal gear 130, it will cause the rotary disc 120 to slide or rotate against the friction, thereby absorbing the impact energy.
The groove 131 within which the rotary disc 120 is fitted is formed away from teeth 132 of the internal gear 130 in an axial direction (i.e., a lateral direction, as viewed in the drawing) of the starter, thus resulting in an increased length of the internal gear 130. In a case where the starter is of a speed-reducing type designed to output a higher torque, the internal gear 130 is usually made of a high strength metal such as a sintered steel, thus resulting in an increased size of the internal gear 130, which leads to an increase in production cost of the starter.